Hot water heater systems and methods for controlling electronic mixing valves

ABSTRACT

Hot water heater systems including electronic mixing valves and methods for controlling such valves are provided. An electronic mixing valve provides a flow of water in a mixed output line. A method includes monitoring an input temperature of cold water supplied to the valve, storing a value of the input temperature, and setting a position limit of the valve based on the stored value, wherein the position limit of the valve is greater than a fully closed position of the valve and less than a fully open position of the valve.

FIELD OF THE INVENTION

The present disclosure relates generally to hot water heater systems,and more particularly to methods for controlling electronic mixingvalves of hot water heater systems.

BACKGROUND OF THE INVENTION

Mixing valves in hot water heater systems are generally used to increasethe hot water capacity of hot water tanks of the hot water heaters. Byincreasing the temperature of the hot water in the hot water tank, andthen mixing the hot water flow from the hot water tank with cold waterin a mixing valve, the realized capacity of the hot water tank isincreased.

However, improvements could be made to presently known methods forcontrolling such mixing valves. For example, improvements to theresponse time for outputting a desired water temperature from a hotwater heater that utilizes a mixing valve could be advantageous. Manypresently-known mixing valves are operated by controllers which utilizeproportional, integral and derivative gains and temperature tolerances.In some cases, such controllers and electronic mixing valves can enteroscillatory states.

Accordingly, improved hot water heater systems and methods forcontrolling electronic mixing valves are desired. In particular,improvements such as but not limited to reducing the range of movementof the valve would result in advantages, such as reduced wear on thevalve, reduced temperature oscillation, decreased response time,improved mixing performance, and improved fault detection.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

In one exemplary embodiment, a method of controlling an electronicmixing valve for a hot water heater, the electronic mixing valveproviding a flow of water in a mixed output line, is provided. Themethod includes monitoring an input temperature of water supplied to thevalve, storing an extremum of the input temperature, setting a positionlimit of the valve based on the stored extremum, wherein the positionlimit of the valve is greater than a fully closed position of the valveand less than a fully open position of the valve, and operating thevalve within a range constrained by the position limit of the valve.

In another exemplary embodiment, a method of controlling an electronicmixing valve for a hot water heater, the electronic mixing valveproviding a flow of water in a mixed output line, is provided. Themethod includes monitoring an input temperature of cold water suppliedto the valve, storing a value of the input temperature, setting aposition limit of the valve based on the stored value, and operating thevalve within a range constrained by the position limit of the valve.

In another exemplary embodiment, a hot water heater is provided. The hotwater heater includes a cold water supply, a hot water tank, anelectronic mixing valve, the valve connected to the cold water supply,the hot water tank, and a mixed output line, the valve operable toreceive variable input from each of the cold water supply and the hotwater tank and to provide a mixed output flow of water in the mixedoutput line, a motor in communication with the valve, the motor operableto move the valve between a fully open position and a fully closedposition, a temperature sensor operable to sense the temperature in oneof the cold water supply and the hot water tank, and a controller inoperative communication with the temperature sensor and the motor, thecontroller operable to monitor the sensed temperature, store an extremumof the sensed temperature, and set a position limit of the valve basedon the stored extremum, wherein the position limit of the valve isgreater than the fully closed position of the valve and less than thefully open position of the valve.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth in the specification, which makes reference to the appendedfigures, in which:

FIG. 1 is a schematic view of a hot water heater system in accordancewith an exemplary embodiment of the present disclosure;

FIG. 2 is a partial perspective, section view of a hot water heater inaccordance with an exemplary embodiment of the present disclosure;

FIG. 3 is a flow chart illustrating a method for controlling anelectronic mixing valve for a hot water heater in accordance with anexemplary embodiment of the present disclosure;

FIG. 4 is a flow chart illustrating another method for controlling anelectronic mixing valve for a hot water heater in accordance with anexemplary embodiment of the present disclosure; and

FIG. 5 is a flow chart illustrating another method for controlling anelectronic mixing valve for a hot water heater in accordance with anexemplary embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made in detail to embodiments of the invention,one or more examples of which are illustrated in the drawings. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment can be used with another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

U.S. Pat. No. 9,244,466, issued Jan. 26, 2016, entitled “ElectronicMixing Valve in Standard Hot Water Heater,” is incorporated by referencein its entirety herein.

FIG. 1 illustrates an exemplary hot water heater system 100 and hotwater heater 10 therefor. As shown, the hot water heater system 100generally includes hot water heater 10, an electronic mixing valve 20and a controller 30. In the exemplary embodiment of FIGS. 1 and 2, thehot water heater 10 includes a reservoir or water storage tank 12 forstoring water and a heat source 14 for heating the water stored in thetank 12. The tank 12 and heat source 14 are generally housed within acasing 11 of the hot water heater 10. In exemplary embodiments, such asis illustrated in FIG. 2, the hot water heater 10 is a heat pump waterheater, and the heat source 14 is thus a heat pump heating element. Itshould be understood, however, that the present disclosure is notlimited to heat pump water heaters, and rather that any suitable waterheaters may be utilized. Further, any suitable heat sources 14,including gas burners, heat pumps, electric resistance elements,microwave elements, induction elements, or any other suitable heatingelement or combinations thereof, may be utilized. The hot water heater10 includes an inlet 34 for receiving water from inlet line 16 fordelivery into the tank 12. The water in the inlet line 16 is in aninitial non-heated, i.e., “cold,” state, e.g., as supplied from thewater supply line of a home or other building. The hot water heater 10also includes an outlet line 18 for supplying water from the tank 12that has been heated to a pre-determined temperature, generally referredto herein as “hot” water. In the exemplary embodiment shown in FIGS. 1and 2, the outlet line 18 is coupled to the mixing valve 20. Thus, themixing valve 20 receives a cold water input, i.e., non-heated water fromthe inlet line 16, and a hot water input, i.e., heated water from theoutlet line 18, and produces a mixed output in output line 22. Valve 20mixes the hot water input with the cold water input such that the outputtemperature of the water from the mixing valve 20 is reduced withrespect to the temperature of the hot water in tank 12. The mixing valve20 includes a mixed outlet or output line 22 that delivers the mixedoutput water to the portions of the plumbing system 40 to which the hotwater heater 10 is connected, generally referred to herein as the hotwater portions of the plumbing system 40. The plumbing system 40 can bepart of a residential, commercial or other water plumbing system thatincorporates a hot water heater.

In some exemplary embodiments, such as the examples illustrated in FIGS.1 and 2, the mixing valve 20 is fluidly connected to the inlet line 16and the outlet line 18. The mixing valve 20 may be coupled to theplumbing system 40 via the mixed output line 22. As illustrated forexample in FIG. 2, in some exemplary embodiments, the mixing valve 20may be an electronic mixing valve actuated by a motor 26, which may be astepper motor. Suitable stepper motors may include motors configured tomove the valve 20 over a range of discrete positions between a fullyopen position (i.e., supplying only hot water from within the tank 12)and a fully closed position (i.e., supplying only cold water from inletline 16). For example, the fully closed position may correspond to stepzero and the fully open position may correspond to any number, e.g.,ten, or in some exemplary embodiments it may go up to eleven.Additionally, some exemplary embodiments may include a stepper motor 26that ranges up to five thousand steps or more, i.e., in some exemplaryembodiments the fully open position may correspond to step fivethousand, and in such exemplary embodiments a half-open position maycorrespond to step two thousand five hundred. In other exemplaryembodiments, the mixing valve 20 may include for example, a solenoidoperated water valve or a gear or motor driven water valve. In alternateembodiments, any suitably controlled water mixing valve can be utilizedto provide precise flow control such as for example, a servo motorcoupled with a valve.

In exemplary embodiments, the mixing valve is disposed within the casing11, such as is illustrated in FIG. 2. Alternatively, however, the mixingvalve may be external to the hot water heater 10.

In some exemplary embodiments, such as those shown in FIGS. 1 and 2, thecontroller 30 may be an electronic controller that is operativelycoupled to the hot water heater 10 and the mixing valve 20. Controller30 may include or be operatively coupled to, or be in communicationwith, one or more processor(s) that are operable to monitor and controlthe flow of hot water from the hot water tank 12 and heated water fromthe mixing valve 20, as well as execute the processes that are generallydescribed herein. In one embodiment the controller 30 can include orreceive machine-readable instructions that are executable by one or moreprocessors or other suitable processing device(s). The processor(s) caninclude program code to perform particular tasks and/or datamanipulations, as are generally described herein. In one embodiment, theprocessor(s) can include or be coupled to a memory and input/outputdevices. The memory typically includes both non-volatile memory, such assemiconductor type random access memory, and non-volatile memory, suchas a magnetic computer disk.

In some exemplary embodiments, the controller 30 may be operativelycoupled to and between, and in communication with, the hot water heater10 and the mixing valve 20. For example, the controller 30 may controlthe mixing valve 20 to increase or decrease the temperature of the waterin the mixed output line 22. This can include, for example, regulatingone or more valves that are part of or coupled to the mixing valve 20 toincrease or reduce the amount of hot water from the tank 12 that isbeing supplied to the mixing valve 20 or that flows through mixing valve20 to mixed output line 22.

The controller 30 may also include or be coupled to a user interface 32.In some exemplary embodiments, the controller 30 and user interface 32may form part of a home energy management (HEM) system. The userinterface 32 may comprise any suitable control or display that willallow a user to program, set and adjust the functions and settings ofthe hot water heater system 100, as are generally described herein. Insome exemplary embodiments, the user interface 32 may comprise a displayinterface, such as a touch screen display. In some exemplaryembodiments, the user interface 32 may also or instead include buttonsor switches for manipulating and programming the settings of the system100, including, for example, the set-point temperature. In someexemplary embodiments, the user interface 32 may comprise or be part ofa control panel for the hot water heater 10. The user interface 32 mayalso be located remotely from the hot water heater 10, and may beaccessible through a computing device or a web based interface.

In some exemplary embodiments, such as illustrated in FIGS. 1 and 2, thesystem 100 includes one or more temperature sensors 24 for detecting andmonitoring the temperature of the water in the different portions of thesystem 100. In the exemplary illustrations of FIGS. 1 and 2, sensors 24,which may be thermistors, thermocouples, resistance temperaturedetectors, or other temperature sensors, are shown on or thermallycoupled to one or more of the inlet line 16, the outlet line 18, mixedoutput line 22 and the hot water tank 12. The sensor(s) 24 are generallyconfigured to provide one or more signals or commands to the controller30 that will allow the controller 30 to detect and determine temperaturevalues for the water in various portions of the hot water system 100.For example, a hot water input temperature may be measured in tank 12(See, e.g., FIG. 2) and/or in supply line 18 (See, e.g., FIG. 1).

In some exemplary embodiments, the sensors 24 may be coupled to thecontroller 30 via a wired or wireless communication connection orinterface. For purposes of the description herein, wirelesscommunication connections and interfaces can include, but are notlimited to, wireless radio, WI-FI, BLUETOOTH, ZIGBEE and Ethernetwireless type devices and interfaces.

The behavior of the mixing valve 20 (i.e., output temperature as afunction of valve position) may not be linear or consistent depending onflow rate, water temperatures, water pressure or any other variousparameter. In such instances, behavior of valve 20 may not be wellsuited for calculating based on a formula or equation. Thus, in someexemplary embodiments, it may be advantageous to empirically determinethe valve characteristics. Nonetheless, it is within the scope of thepresent subject matter to develop a correlation between valve positionand output temperature through other means, e.g., calculating based on aformula, which may be suitable for some instances wherein parameterssuch as flow rate, water temperature, and/or water pressure arerelatively consistent.

The output temperature from mixing valve 20 depends on several otherfactors in addition to the valve position, such as the hot water inputtemperature and the cold water input temperature, that can vary overtime. For example, during non-flow or standby periods, when hot water isnot being consumed from the hot water tank 12, the water temperature ator near the inlet 34 may become elevated due to conduction from the tank12. In such cases, the input temperature of “cold” water supplied tomixing valve 20 will be highest at the beginning of a draw, especiallywhen that draw occurs after a long standby time. During a draw, as therelatively warm water in inlet 34 is flushed out by colder water, theinput temperature of “cold” water supplied to mixing valve 20 maydecrease non-linearly, e.g., asymptotically, over a period of time untila minimum temperature is reached. Accordingly, in such cases, therequired minimum open position for the valve (i.e., minimum amount ofhot water input to achieve the desired output temperature) varies overtime, e.g., as the cold input temperature decreases, the minimum openposition increases. In some exemplary embodiments, a lookup table whichcorrelates temperature values and valve positions may be provided, e.g.,may be programmed into memory associated with controller 30. Forexample, the lookup table may associate a certain value for thetemperature of incoming cold water in line 16 with the correspondingvalve position of the mixing valve that results in a desired temperaturein the mixing valve output line 22. In exemplary embodiments whereinvalve 20 is actuated by a stepper motor 26, a minimum open position maybe, e.g., step 60 out of 100 to output the desired temperature when thecold input temperature is at its lowest. Thus, the controller 30 may insome exemplary embodiments be operable to initialize at a predeterminedminimum open value that is greater than a fully closed position of thevalve, e.g., in embodiments where valve 20 is actuated by a steppermotor 26, the starting point can be greater than zero, which results inreduced operating range of the valve with concomitant reduction in wearon the valve components, as well as decreased response time, among otheradvantages. For example, the controller 30 may in some embodiments be aproportional-integral-derivative (PID) controller, in such embodimentsthe PID loop can be constrained by, e.g., a certain minimum which isgreater than a fully closed position of the valve and/or a certainmaximum which is less than a fully open position of the valve. Suchconstraining extrema may be predetermined, either empirically ortheoretically, and stored in a lookup table wherein they are correlatedor otherwise associated with at least one external parameter, e.g., coldwater input temperature or hot water input temperature.

As another non-limiting example of the potential advantages of thepresent subject matter, improved fault detection can be provided. Afault condition such as a stuck valve may be indicated if thetemperature does not stabilize within the normal response time. Thus,because the normal response time, i.e., the time it takes from thebeginning of a hot water draw until the temperature stabilizes, isreduced, the time it takes to detect, e.g., a stuck valve, may also bereduced.

Referring now to FIGS. 3 and 4, various exemplary embodiments of methodsfor controlling electronic mixing valves 20 for hot water heater systems100 are provided. In general, such methods provide improved operation ofcontrollers 30, electronic mixing valves 20, and systems 100 in general.For example, such methods may reduce the risk of electronic mixingvalves 20 encountering unstable conditions and entering oscillatorystates. Further, such methods may reduce the response time of the system100, e.g., the time required to provide the desired water temperature inoutput line 22.

It should be noted that controllers 30 as disclosed herein are capableof and may be operable to perform any methods and associated methodsteps as disclosed herein.

For example, referring to FIG. 3, a method 200 for controlling anelectronic mixing valve 20 for a hot water heater system 100 mayinclude, for example, the step 210 of monitoring at least one inputtemperature of water supplied to the mixing valve 20. The inputtemperature may be the cold water input temperature and/or the hot waterinput temperature. The input temperature(s) may be determined based onsignals received from the temperature sensor(s) 24, and may becontinuously or regularly monitored by controller 30.

Method 200 may further include, for example, the step 220 of storing avalue of the input temperature. The stored value can generallycorrespond to the temperature being monitored in exemplary embodiments.That is, when the monitored temperature is the cold water inputtemperature, the stored value may be a minimum temperature, and when themonitored temperature is the hot water input temperature the storedvalue may be a maximum temperature. In some exemplary embodiments, thestored value may be a daily value, e.g., when the stored value is aminimum, the daily minimum temperature for each day in a set of days maybe stored. The set of days for which values of stored may be about threedays to about thirty days. In some exemplary embodiments, the storedvalue may be stored within a moving seven-day window, that is, uponstart up a daily value may be stored every day for the first seven days,and beginning on the eighth day a new value is added to the stored seteach day and the oldest value is discarded. Thus, the operative valuemay be the outlying value within a limited time frame, e.g., theoperative stored minimum based upon which the position limit isdetermined may be the lowest daily minimum over a moving seven-daywindow. In such exemplary embodiments, seasonal variations intemperature can be accounted for, e.g., a minimum temperature valuestored in January is unlikely to be valuable in July in most cases.

Method 200 may further include, for example, the step 230 of looking upa predefined position limit associated with the stored minimum ormaximum in a lookup table. As illustrated in FIG. 3, various exemplaryembodiments may include looking up a predefined position limitassociated with the stored minimum or looking up a predefined positionlimit associated with the stored maximum, or looking up predefinedposition limits associated with both a stored minimum and a storedmaximum. The lookup table can be derived empirically or may containtheoretical or unobserved correlations between output temperature andvalve position. One possible process to empirically characterize thevalve may include determining an input temperature of water supplied tothe valve, moving the valve between a fully closed position and a fullyopen position while monitoring the mixed output temperature, andcorrelating the mixed output temperature with the relative position ofthe valve. Then, a position limit of the valve may be defined based onthe correlation of the mixed output temperature and the relativeposition of the valve, wherein the defined position limit of the valvecorrelates to the desired output temperature. The defined position limitmay also, in some exemplary embodiments be associated with the inputtemperature in a lookup table. The lookup table may include multipleposition limits associated with a range of input temperatures. Forexample, four position limits may be provided in a lookup table, with aposition limit associated with each of four ranges of inputtemperatures, e.g., for cold water input temperature, such ranges maybe, below forty-five degrees Fahrenheit (<45° F.), between forty-fivedegrees Fahrenheit and seventy degrees Fahrenheit (45° F. to 70° F.),between seventy degrees Fahrenheit and ninety degrees Fahrenheit (70° F.to 90° F.), and above ninety degrees Fahrenheit (>90° F.).

Method 200 may further include, for example, the step 240 of setting atleast one position limit of the valve to the predefined position limitassociated with the stored minimum or maximum. The position limit isgreater than a fully closed position of the valve and less than a fullyopen position of the valve. Method 200 may further include the step 250of operating the valve within a range constrained by the position limitof the valve. Thus, the operating range of the valve 20 may beadvantageously constrained, as discussed above.

Another exemplary method 300, as illustrated in FIG. 4, may include thestep 310 of monitoring an input temperature of water supplied to mixingvalve 20, the step 320 of storing a value of the monitored inputtemperature, the step 330 of looking up a predefined position limitassociated with the stored value in a lookup table, the step 340 ofsetting a position limit of the valve to the predefined position limitassociated with the stored value in the lookup table, and the step 350of operating the valve within a range constrained by the position limitof the valve.

The several exemplary embodiments illustrated and described herein areby way of example and without limitation. Features illustrated ordescribed as part of one embodiment can be used with another embodimentto yield a still further embodiment. In various exemplary embodiments,the temperature monitoring step may include monitoring the temperatureof the hot water input and/or the cold water input. Further, variousexemplary embodiments may include storing one or more values of themonitored temperature. That is, in various exemplary embodiments, thecold water input temperature may be monitored and a minimum thereofstored, while the hot water input temperature may also or instead bemonitored and a maximum thereof stored, or in other exemplaryembodiments, both the cold water input temperature and the hot waterinput temperature may be monitored and an average temperature value maybe stored. Additional other variations and combinations of features aswould be recognized by one of ordinary skill in the art from theexamples illustrated and described herein are possible and all arewithin the scope of the present subject matter.

One possible combination of the various embodiments is illustrated forexample in FIG. 5. As illustrated in FIG. 5, such exemplary method 400includes an embodiment wherein the input temperature is cold water inputtemperature, the stored value is a minimum temperature, the controller30 includes a PID control loop, and motor 26 is a stepper motor with arange from zero to six thousand. In this particular exemplaryembodiment, method 400 may include a step 410 of measuring cold waterinput temperature (T_(COLD)), a step 420 of comparing the measuredT_(COLD) to a stored minimum value of T_(COLD), and a step 430 ofstoring the minimum value of T_(COLD). Also illustrated for example inFIG. 5, the method 400 may further include a step 440 of comparing thestored minimum value to a set of four ranges of values (e.g., in alookup table according to the example as discussed above in paragraph33) and a step 450 of setting a minimum valve position (e.g., PID lowerlimit in this example) based on the stored value of T_(COLD).

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. A method of controlling an electronic mixingvalve for a hot water heater, the electronic mixing valve providing aflow of water in a mixed output line, the method comprising: monitoringan input temperature of water supplied to the valve from a cold watersupply; storing a minimum of the input temperature; looking up apredefined position limit associated with the stored minimum in a lookuptable; setting a position limit of the valve to the predefined positionlimit; and operating the valve within a range constrained by theposition limit of the valve; wherein the position limit of the valve isgreater than a fully closed position of the valve and less than a fullyopen position of the valve.
 2. The method of claim 1, wherein the storedextremum is a daily extremum.
 3. The method of claim 1, wherein the stepof storing an extremum of the input temperature further comprisesstoring the extremum within a moving seven-day window.
 4. The method ofclaim 1, wherein the predefined position limit is a minimum openposition, and the step of looking up a predefined position limitcomprises looking up a predefined minimum open position associated withthe stored minimum temperature in a lookup table, and setting theminimum open position of the valve to the predefined minimum openposition.
 5. A method of controlling an electronic mixing valve for ahot water heater, the electronic mixing valve providing a flow of waterin a mixed output line, the method comprising: monitoring an inputtemperature of cold water supplied to the valve; storing a value of theinput temperature; looking up a predefined position limit associatedwith the stored value in a lookup table; setting a position limit of thevalve to the predefined position limit; and operating the valve within arange constrained by the position limit of the valve.
 6. The method ofclaim 5, wherein the position limit of the valve is a minimum openposition.
 7. The method of claim 5, wherein the stored value is a dailyminimum temperature.
 8. The method of claim 5, wherein the stored valueis a daily maximum temperature.
 9. The method of claim 5, wherein thestored value is a daily average temperature.
 10. A hot water heater,comprising: a cold water supply; a hot water tank; an electronic mixingvalve, the valve connected to the cold water supply, the hot water tank,and a mixed output line, the valve operable to receive variable inputfrom each of the cold water supply and the hot water tank and to providea mixed output flow of water in the mixed output line; a motor incommunication with the valve, the motor operable to move the valvebetween a fully open position and a fully closed position; a temperaturesensor operable to sense the temperature in one of the cold water supplyand the hot water tank; and a controller in operative communication withthe temperature sensor and the motor, the controller operable to monitorthe sensed temperature, store an extremum of the sensed temperature,look up a predefined position limit associated with the stored extremumin a lookup table, set a position limit of the valve to the predefinedposition limit, and operate the motor to move the valve within a rangeconstrained by the position limit of the valve, wherein the positionlimit of the valve is greater than the fully closed position of thevalve and less than the fully open position of the valve.
 11. The hotwater heater of claim 10, wherein the temperature sensor is operable tosense the temperature in the cold water supply, and the controller isoperable to store a minimum of the sensed temperature and set a positionlimit of the valve based on the stored minimum by looking up apredefined minimum open position associated with the stored minimumtemperature in a lookup table, and setting the minimum open position ofthe valve to the predefined minimum open position.
 12. The hot waterheater of claim 10, wherein the temperature sensor is operable to sensethe temperature in the hot water tank, and the controller is operable tostore a maximum of the sensed temperature and set a position limit ofthe valve based on the stored maximum by looking up a predefined maximumopen position associated with the stored maximum temperature in a lookuptable, and setting the maximum open position of the valve to thepredefined maximum open position.